Recent scientific studies have proven that many hand tools and other similar devices may be much more damaging to the users than what is commonly attributed to injuries from accidents and/or improper use. The injuries referred to are not necessarily the fault of the user at all; but rather, the improper design of some tools and devices that lead to cumulative-effect traumas such as carpal tunnel syndrome, tenosynovitis, "Trigger Finger", inschemia, vibration-induced white finger and tennis elbow. These injuries commonly result from work requiring repetitive use of certain non-ergonomically designed tools over extended periods of time. The only way to reduce the occurrences of these types of injuries are for users to not use the injury producing tools as frequency and use only an ergonomically-correct type of tool that takes into consideration the effects of repetitive use. A reduction in frequency of use is not a viable option for the many individuals whose work relies on such use, therefore the only real solution is to develop better designed hand-operated tools.
As discussed above, the cumulative-effect traumas are the principle injuries caused from the improper design of tools. Tools that are particularly culpable are the hand-operated type of power tools, such as drills, saws, sanders and the like. These tools, because of the unbalanced design of their housings, handles and/or grips, do not compensate for the minimal or often, complete lack of support alloted the hand, wrist or forearm of the user. This lack of support does not allow for the tool to be held in a safe manner commensurate with extended duration. Because of the weight and the trepidations that occur during use of the tool, the hand will naturally bend at the wrist due to the absence of sufficient strength in the wrist and the forearm muscles which are used to support the tool's weight. After prolonged use this can lead to a number of potential work injuries. In order to properly understand the potential injuries and their causes, a rudimentary explanation is necessary of the relationships of the hand, wrist and forearm structures and their single and combined efforts which are applied during hand tool use.
The hand 90, fingers 90A, writs 90B and the forearm 90C is a complex structure comprised of bones 90D, arteries 90E, nerves 90F, ligaments 90G, and tendons 90H, as shown in FIG. 17. The fingers 90A are flexed by muscles in the forearm 90C. The muscles are connected to the fingers 90A by tendons 90H, which pass through a channel in the wrist. This channel is formed by the bones of the back of the hand on one side and the traverse carpal ligament 90G (flexor retinaculum) on the other. The resulting channel is called the carpal tunnel. Through this tunnel pass many vulnerable anatomic structures including the radial artery 90E and median nerve 90F. Running along the outside of the transverse carpal ligament 90G are the ulnar artery 90E and ulnar nerve 90F. This artery and nerve pass beside a small bone in the wrist called the pisiform bone 90D. The bones of the wrist connect to the two long bones of the forearm 90C--the ulna and the radius. The radium connects to the "thumb side" of the wrist and the ulna connects the "little finger side" of the wrist. The configuration of the wrist joint permits a neutral position 90I and movements in only two planes, each one at an approximate 90.degree. angle to the other as shown in FIG. 18. The first plane allows palmar flexion 90J or, when it is performed in the opposite direction, dorsiflexion 90K. The second movement plane consists of either ulnar deviation 90L or radial deviation 90M of the hand 90. The ulna and radius of the forearm connect to the humerus of the upper forearm and the bicep muscle connects to the radius. When the forearm 90C is extended, the bicep muscle will pull the radius strongly against the humerus. This can cause friction and heat in the joint. The bicep muscle is both a flexor of the forearm and an outward rotator of the wrist. Whenever the forearm 90C is bent at 90.degree. at the elbow and the wrist 90B is rotated outward, the bicep muscle contracts and bulges. This action, necessitates sufficient support to maintain a hand operated tool at a constant level. Also, simultaneous inward rotation of the hand, to direct the motion of the tool, are predominantly required in any hand tool use or application. However, when considering the damaging effects this repetitive motion produces, it should be considered in the design of the hand tool.
The flexor tendons of the fingers pass through the carpal tunnel of the wrist. When the wrist is aligned with the forearm, there is little change of injury. However, if the wrist is bent, especially in palmar flexion 90J or ulnar deviation 90L (or both) as shown in FIG. 18, problems can occur. The continued us of tendons that bend and bunch-up in the carpal tunnel, will cause tenosynovitis--an inflammation of the tendons and their sheaths.
Another form of tenosynovitis, known as "Trigger Finger", can develop if the index finger is used excessively for operating triggers switches when there is undue stress being exerted on other areas of the hand 90, wrist 90B or forearm 90C. The strength that would normally be directed to the index finger deviates to compensate for its necessity in the other areas. "Trigger Finger" is characterized by the afflicted person being able to flex but not extend the finger actively. The finger must be passively straightened, and when it is an audible click may be heard. This is caused by the distal phalanx (segment) of the finger having to be flexed while the middle phalanx is kept straight. One way to minimize this injury is to use the thumb or middle finger instead of the index finger to operate the trigger switch. The thumb is the only finger that is flexed, abducted and opposed by strong, short muscle located entirely within the palm of the hand as stated above. This would be a good way to avoid injury but for most hand tools operations, it is not considered feasible. In order to properly direct the motion of certain hand tools (especially those which are operated by way of power), the user must use the thumb to grip the tool and support its weight.
In addition to tenosynovitis, carpal tunnel syndrome can also develop. Carpal tunnel syndrome is a disorder caused by injury of the median nerve 90F where it passes through the carpal tunnel of the writs 90B. The symptoms include numbness, loss of feeling and grip, and finally muscle atrophy and loss of hand functions. This condition occurs three to ten times more often in women than in men, reflecting either a physiological-anatomical difference or only the fact that women are more likely to engage in work that requires repetitive bent-wrist matters.
A general practice in hand tool use is to avoid ulnar deviation 90L and radial deviation 90M as shown in FIG. 18. Radial deviation is another movement associated with hand tool use which can also lead to injury. This movement, particularly if combined with palmar flexion 90J and dorsiflexion, 90K increases pressure between the head of the radius and the capitulum of the humerus of the elbow. Avoidance of these damaging movements is accomplished by using tools which have a support attached, that acts as a plane to maintain a straight hand, wrist and forearm when the tool is in use. In addition to the hand, wrist and forearm support, handles should be designed with a slight upper-forward inclination that follows the natural angular inclination of the hand and a large contact surface. This will act to distribute over a larger area, the damaging effect which the weight of the tool imposes and to direct some stress to less-sensitive areas, such as the stronger tissue between the thumb and index finger.
Designing tools for safe operation in general would be a reason itself for attaching the pre-stated support that would substantially lower the occurrence of the damaging movements of the hand, wrist and forearm. By eliminating the need for the body to redirect support to areas that should not require it, the high-stress areas would receive the strength to function in an injury-free manner. The hand, 90 wrist 90B and forearm 90C could also gain strength because the support forces the maintaining of a straight-plane grip. The incentive design includes a drill housing that has the longitudinal axis of the attached drill bit in alignment with the longitudinal axis of the forearm and the fist grasping the handle of the housing. This longitudinally aligned design, in combination with the inventive hand, wrist and forearm support, avoids abnormal angular and rotational displacement between the hand and wrist and helps to minimize incidents of the above discussed problems. As described above, this eliminates the excessive stress induced from using tools while the wrist is bent and directs the necessary strength to the index finger, when a trigger action must be used.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention, however, the following U.S. Pat. Nos. were considered related:
______________________________________ PATENT NO. INVENTOR ISSUED ______________________________________ Des. 326,597 Lee 2 June 1992 84105047.9 (EP) Berry et al (Pub) 0,127,014 2,525,588 Cameron et al 10 October 1950 712,843 Paul 4 November 1902 ______________________________________
The Des. 326,597 Lee patent discloses a design for a power wrench. The wrench features an extended working arm having at its front end, a 360-degree rotating gripping section. The hand grip includes a power switch located at the front of the grip that is actuated by the fore finger. Extending from the loser back section of the hand grip, is a rod having at its back section an arm rest and an adjustable arm strap.
The 84105047.9 (EP) Berry et al patent discloses a hand grip for hand tools such as a power drill. The grip has a generally bulbs shape having an upper notch that allows the ball of the thumb to be placed therein. The grip also includes on its front section an upper groove and a lower edge that allows the three fingers of the hand to be comfortably wrapped around the grip. When the grip is grasped, the compressive forces produced by the hand are evenly distributed throughout the palm. This allows the hand tool to be maintained in a level configuration to provide maximum leverage and control.
The 2,525,588 Cameron et all patent discloses a portable hand drill. The drill features an electric bulb that is mounted in a passageway located in the front housing of the drill. The light bulb is mounted to direct light towards the drill point and the work area and includes a removable cap along with a focusing lens.
The 712,843 Paul patent discloses a pneumatic sugar-cane cutter. The cutter includes a rod that extends from the back of the cutting section. At the rear end of the rod is attached a curved or concave plate to which the forearm of the user is adapted or otherwise secured by a strap. The plate is pivotally attached to the rod so that, when the user releases the handle, the tool remains supported, permitting the operator free use of the hand.
In summary, the basic differences between the prior art patents and the applicant's invention is in the basic design of the housing which is longitudinally aligned with a hand, wrist and forearm support. In Lee's patent, the working forearm is in obvious misalignment with the hand grip, in Berry's et al patent, the compression forces produced by the hand are evenly distributed throughout the palm. However, the axis of the drill bit is in parallel with the axis of the forearm rotation and is not in alignment as in the applicant's design. In Cameron's et al patent, there is no parallel or direct alignment disclosed. The Paul's patent discloses a forearm and arm plate. However, the entire housing and plate design differs considerably from those of the applicant's invention.
For background purposes and as indicative of the art to which the invention is related, reference may be made to the remaining patents found in the search.
______________________________________ PATENT NO. INVENTOR ISSUED ______________________________________ 5,361,851 Fox 8 November 1994 5,313,735 Latouche 24 May 1994 5,070,576 Banta 10 December 1991 4,924,571 Albertson 15 May 1990 Des. 303,204 Marks 5 September 1989 4,779,687 Schreiber et al 25 October 1988 4,604,005 Russ 5 August 1986 2,138,348B (GB) Andersson 16 July 1986 56-56313 (JP) Kishi 18 May 1981 2,504,880 Rittenhouse 18 April 1950 ______________________________________